The invention generally pertains to voltage converters. More particularly, the invention concerns DC/DC voltage converters with fault protection.
Vacuum fluorescent displays (VFD""s) used, for example, in automotive applications commonly require an input voltage that is greater than the DC voltage available from the vehicle battery or charging system. Typical vehicles provide approximately 14 to 15 volts DC, while it is not uncommon for VFD""s used in radio, instrument cluster or other display device applications to require greater than 50 volts in order to operate properly. To provide such an increased voltage over that available from the automotive system in which the display is operating, a DC to DC boost converter is used. Such a converter xe2x80x9cboostsxe2x80x9d the voltage delivered to the display, such as a VFD, to a voltage greater than that of the vehicle supply.
Prior approaches to implementing DC to DC converters feature two basic methods of generating the required increased voltage. In a first prior approach, circuitry consisting of a switching regulator controller integrated circuit, also known as a DC to DC controller xe2x80x9cICxe2x80x9d which generated a pulse width modulated (PWM) wave form was used to switch the input supply current through an inductor or transformer and to use the energy stored in the inductor or transformer to increase voltage delivered to the display to a level greater than the input supply voltage. Such prior DC to DC controller ICs also provided a feedback mechanism for monitoring the converter output voltage and adjusting the PWM waveform so as to regulate the voltage supplied to the converter output while maintaining proper operating voltages for which the circuit was designed. This conventional type of IC was specifically designed for DC to DC power supplies and typically included an oscillator, PWM generation circuitry, a feedback comparator circuit, and, in some cases, a switching transistor through which the inductor or transformer current was switched. This prior method operated at a fixed oscillation frequency set by discrete components and generated only a preselected output voltage. Any change in operating frequency or output voltage requirements dictated a change in the discrete components.
In a second prior approach, circuitry consisting of all discrete components with no integrated circuits generated a PWM waveform. The circuitry additionally implemented appropriate oscillator and feedback apparatus to control the switching of current through an inductor or transformer in such a way as to use the energy stored in the inductor or transformer to increase the voltage supplied to the converter output to a level greater than that of the supply voltage. This discrete circuitry additionally regulated the converter output voltage in accordance with design intents. This prior approach also operates at a fixed oscillator frequency and fixed output voltage, with any change in parametric operation requiring a change in the actual discrete circuit components.
Therefore, there is seen to be a need in the art for a DC/DC converter arranged in such a way that modifications to the desired operating characteristics can be carried out in a more facile manner.
Accordingly, a voltage converter comprises a direct current input voltage source, a voltage transforming element having an input coupled to the input voltage source and an output presenting a voltage signal thereon, a switching element coupled to the voltage transforming element for intermittently interrupting current flow from the input voltage source to the voltage transforming element, a converter output coupled to the output of the voltage transforming element via a rectifier and adapted to present a converter output voltage to a load, and a programmable controller having an input coupled to the converter output and an output coupled to the switching element, the programmable controller operative to control switching states of the switching element in accordance with preselected programmable operating parameters of the voltage converter.
In another aspect of the invention, a DC/DC voltage converter comprises a direct current input voltage source, a transformer having primary and secondary windings, the primary winding being coupled to the input voltage source, a switching transistor coupled to the primary winding and operative in a first switching state to allow current flow from the input voltage source through the primary winding and operative in a second switching state to inhibit said current flow, a converter output coupled to the transformer secondary winding via a rectification circuit and adapted to present a converter output voltage to a load, and a microprocessor-based controller having an input coupled to the rectification circuit and an output coupled to the switching transistor, the controller operative to selectively place the switching transistor in its first and second switching states in accordance with preselected, programmable operating parameters of the voltage converter.